Although I don't think the decline of USENET was caused by worries about the inability of governments to control it, I can answer your question.

USENET has no central point of control (or at least it had none 15 years ago when I lost interest in USENET). The basic infrastructure is designed so that any news server can get a copy of all the USENET articles being stored by any other news server, and anyone with sufficient bandwidth and sysadmin skills can set up a news server. Consequently, there's no single organization that has the power to remove an article from USENET unless perhaps it is an organization that has arisen since I lost interest in USENET 15 years ago that is central to the control of USENET spam. (I mention spam because 15 years ago, spam was the only potential reason or problem an effective alliance of server owners might recognize as a legitimate reason to remove a message from USENET.) It would have to be an organization that every significant news server relies on for telling spam from non-spam. But I get the impression that spam is out of control on USENET, which is a strong sign that such a universally-consulted spam-control organization does not exist.

Anyway, I hope that you get the idea of what the OP was on about with his implication that pro-censorship forces killed USENET because government could not control speech on USENET (which, again, probably does not have any basis in reality because IMHO USENET was never popular enough with readers to worry pro-censorship forces).